1. Field of the Invention
This invention relates to emergency call systems (e.g., E9-1-1), including wireless and Internet Protocol (IP) based Voice Over Internet Protocol (VoIP) emergency call systems, that rely on non-call associated signaling in order to provide location data.
2. Background of the Related Art
9-1-1 is a phone number widely recognized in North America as an emergency phone number that is used to contact emergency dispatch personnel. Enhanced 9-1-1 (E9-1-1) is defined by an emergency call being selectively routed to an appropriate PSAP, based on a special identifier (P-ANI, or “Pseudo Automatic Number Identifier”, also referred to as “ESxK”), and includes the transmission of callback number and location information when 9-1-1 is used. E9-1-1 may be implemented for landline, cellular or VoIP networks. A Public Service Answering Point (PSAP) is a dispatch office that receives 9-1-1 calls from the public. A PSAP may be a local, fire or police department, an ambulance service or a regional office covering all services. As used herein, the term “PSAP” refers to either a public safety access point (PSAP), or to an Emergency Call Center (ECC), a VoIP term.
Regardless of the network type, a 9-1-1 service becomes E-9-1-1 when automatic number identification and automatic location information related to the call is provided to the 9-1-1 operator at the PSAP. A primary challenge results from the fact that calls may arrive at the PSAP without the caller's actual callback number or location information displayed at the emergency operator's terminal.
FIG. 3 shows a conventional landline public safety access point (PSAP) to automatic location identifier (ALI) connection.
In particular, FIG. 3 shows a PSAP 400 connected to one Automatic Location Identifier (ALI) database 401. Upon receiving a 9-1-1 call, the PSAP 400 queries the ALI 401 for location data. The ALI database 401 accepts the query from the PSAP 400 for location. The query includes the telephone number of an emergency caller. The ALI database 401 relates the received telephone number to a physical street address and provides that street address (location information) back to the PSAP 400 in a manner that works for the customer premise equipment (CPE) display at the PSAP 400.
An ALI is typically owned by a local exchange carrier (LEC) or a PSAP, and may be regional (i.e. connected to many PSAPs) or standalone (i.e. connected to only one PSAP). There is currently no one single standard interface protocol for PSAP-ALI connection/communication.
FIG. 4 shows a context diagram for a conventional non-landline positioning center (e.g., an Internet based voice over Internet Protocol (VoIP) positioning center).
In particular, the ALI database 401 includes a conventional emergency services key (ESQK or ESRK) in a location request sent to an appropriate positioning center 402 (XPC). The emergency services key (ESQK or ESRK) is used by the positioning center 402 as a key to look up the location and other call information associated with the emergency call.
In non-landline telephony, the PSAPs 400 query the ALI 401 for location information. However, the ALI 401 is not pre-provisioned with location data for non-landline calls (e.g. cellular, VoIP etc) and must communicate with other network entities to obtain and deliver location data to the PSAP 400.
Non-landline telephony standards (e.g. cellular, VoIP etc) have mandated that ALIs 401 maintain connectivity to a positioning center 402 that is able to provide current location data for a non-landline call. In the current state of technology, the positioning center 402 provides the caller's location and the callback number to the ALI, which passes it to the requesting PSAP. As can be seen in FIG. 4, an ALI may maintain connectivity to more than one positioning center via multiple interface types—both standard and non-standard (e.g. NENA-02, E2/E2+N-E2(ESP), PAM, etc.).
As used herein, the generic term “XPC” refers interchangeably to any standards-based positioning center. As examples, a positioning center 402 may be any one of the following types used in non-landline networks:                GMLC (Gateway Mobile Location Center): The positioning center that retrieves, forwards, stores and controls emergency position data within the GSM location network.        MPC (Mobile Position Center): The positioning center that retrieves, forwards, stores and controls emergency position data within the ANSI location network.        VPC (VoIP Positioning Center): The positioning center which retrieves, forwards, stores and controls emergency position data within the VoIP location network.        
The term “XPC network” is used herein when appropriate to refer to any non-landline network where a positioning center 402 responds to ALI queries including an emergency services key for location, e.g., cellular, VoIP etc.
So, whether landline or non-landline, conventional emergency call centers, e.g., public safety access points (PSAPs) 400, use emergency services keys such as an emergency services query key (ESQK) or an emergency services routing key (ESRK), collectively referred to herein as ESxK, to query for location information. An emergency service key identifies an emergency call, and is associated with a particular selective router 417 associated with a given public safety access point (PSAP) 400. The emergency services keys ESQK and ESRK are conventionally used to query the automatic location identification (ALI) database 401 for the location of a given emergency caller. An emergency services key is delivered to the E9-1-1 selective router 417 and is the calling number/ANI for the call to the PSAP 400. The emergency services key is used by a selective router 417 as a key to selective routing data associated with the emergency call. The emergency services key is delivered by the selective router 417 to a PSAP 400 as the calling number/ANI for the emergency call, and is subsequently used by the PSAP 400 to request automatic location information (ALI) information indicating the location of the device making the emergency call. Conventional emergency service keys conform to ten-digit North American Numbering Plan Number definitions.
Existing, standardized solutions prescribe a finite pool of emergency services keys (ESQK and ESRK) which are allocated individually, one associated for each emergency call in progress. ESxK numbers are used to request updated location information from the ALI 401 while an emergency call is active, and as such, as appreciated by the inventors hereof, are subject to number exhaustion if the number of active emergency calls exceeds the number of ESxKs in the pool. But because ESxKs (ESQKs and ESRKs) are dynamically assigned at the time of call origination, and because the pool of ESxKs is limited, the inventors appreciate that it is possible for the pool of available ESxKs to run out.
For systems which implement ESQK and/or ESRK keys, It is a well known technique to use timers and default ESxKs to avoid problems associated with a limited pool of ESxKs. Timers have been specified and implemented to limit the amount of time that an ESxK can remain allocated to an emergency call, without regard for the actual call duration. For example, if a call continues after the timer has expired, the specific ESxK which was used to obtain updated location information can get reassigned to a new incoming emergency call.
However, timers are based solely on estimated call duration, a value which could be exceeded. Since emergency calls are numerous, and can remain active for long periods of time once initiated, some service providers have increased the number of allocated ESxK pools in an effort to minimize number pool exhaustion. Additionally, reliance on timers requires much larger pools of ESxKs to be allocated, which is an inefficient use of numbers, and may potentially lead to number exhaustion.
The present inventors appreciate that the conventional technique of using timers to expire the ESQK and ESRK allocation could prove to be devastating if a given emergency call using that expiring ESxK is still active. This is especially true if there is updated location information which would help provide emergency assistance to the caller.
Moreover, ESxK numbers must be purchased, so large numbers of ESxKs represent a direct cost to a provider. Also, as requirements for capacity increase, existing systems must often increase the size of the ESQK and ESRK number pool that they purchase, leading to additional costs for ESQK and ESRK number purchases, additional costs to implement, and additional costs to maintain these larger number pool sizes.